Silenes reactivity

A wide variety of other polar reagents had also been shown to add across the silicon-carbon double bond, and trimethylmethoxysilane (see Eq. 22) had been found to be another rather useful reagent for trapping reactive silenes. 

While infrared characterization of several silenes has been carried out, it has not always been possible to assign the observed bands unequivocally. Table II summarizes the available infrared data. The infrared spectra of reactive silenes, generated by the pyrolysis of suitable precursors, have most often been recorded in an argon matrix at 10 K, whereas the infrared... 

Under thermolytic conditions the cycloheptatriene 481 and the silyl enol ether 482 were obtained in 46% and 24% yield, respectively, along with 29% of the unreacted starting compound, the acylpolysilane which is the precursor for the reactive silene (equation 160)". 

In view of the evident reactivity of Brook -type silenes toward carbonyl compounds and the fact that they are generated photochemically from acylpolysilanes, the question arises whether the silenes do react with their precursors. The very reactive silene 507... 

Encounters between silyl radicals in solution or in the gas phase usually result in recombination and disproportionation (45, 46). Disproportionation results in the production of silanes and highly reactive silenes. The disproportionation reaction is thermodynamically favorable because of the formation of a silicon-carbon double bond, which, although subsequently chemically reactive, is worth —39 kcal/mol (44). For pentamethyldisilanyl radicals, disproportionation is kinetically competitive with radical dimerization (46). In an earlier study, Boudjouk and co-workers (47) demonstrated conclusively by isotopic substitution and trapping that the silyl radicals generated by photolysis undergo disproportionation, as well as, presumably, dimerization (Scheme I). In deuterated methanol, the silanes produced were predominantly undeuterated, whereas methoxymethyldiphenylsilane was extensively deuterated in the a position. The results of these experiments strongly implicated the substituted silene produced by disproportionation. 

Precursor of Silene. 1,1-Dimethylsilacyclobutane is pjTO-lyzed at ca. 600 °C to generate 1,1-dtmethylsilene. The highly reactive silene rapidly undergoes dimerization to provide l,3-disila-l,l,3,3-tetramethylbutane.4 C-C4 and C-O multiple bonds are able to trap the silene. The copyrolysis... 

---